Pressure-sensitive recording materials utilizing the coloring reaction of a color former, which is a material forming a color on donating an electron or accepting a proton such as an acid, and a color developer which is a material accepting an electron or donating a proton are well known as described in, for example, U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, and 3,418,250, Japanese Patent Publication (Unexamined) Nos. 28411/74, 44009/75, etc. Exemplary color developers which are used for this purpose are clay materials such as acid clay, active clay, attapulgite, zeolite, bentonite, kaolin, etc.; metal salts of aromatic carboxylic acids; phenolformaldehyde resins, etc.
Furthermore, a printing method of obtaining a colored image by supplying an ink containing a color former or color formers onto a sheet coated with a color developer is well known (e.g., as described in West German Patent Application (OLS) No. 1,939,962).
As described above, various color developers for pressure-sensitive recording materials are known.
However, the use of clays, which are most generally used as color developers for pressure-sensitive recording materials at present, such as acitve clay, acid clay, etc., has the disadvantages that the colored images formed have poor light resistance and water resistance and also lack good stability with the lapse of time. Also, the use of phenol resins has the disadvantages that the developing power is low and the color developer causes yellowing.
The metal salts of aromatic carboxylic acids are known as a color developer without such disadvantages. A color developer sheet using a metal salt of an aromatic carboxylic acid is prepared by coating a support with an aqueous dispersion containing the color developer together with an inorganic pigment, a binder, a dispersing agent, and other additives. However, the color developer sheet obtained in the manner as described above is yet insufficient in coloring speed and developing power and the coating sheet has a coating unevenness caused by the marked formation of bubbles in the aqueous dispersion.